1. Field of the Invention
This invention relates to an improved probe for use in performing a characteristic test of, for example, a semiconductor device. This probe is used in a state where it is in tight contact with an electrode pad of the device so as to be electrically connected to the internal circuit of the device.
2. Description of the Related Art
As is shown in FIG. 1, in manufacturing a semiconductor device such as an LSI, integrated circuits are formed in those chip regions 20 of a disklike silicon wafer 10, the chip regions having a size of a few mm square. The chip regions 20 are then separated from one another. Separated chips 20 are assembled into a finished product by use of a ceramic or resin package. In the case of using the resin package, they are assembled into a mountable form of e.g. DIP type after being subjected to assembling steps such as die bonding, wire bonding, and resin molding.
To minimize the degree of inferior products to be provided after the assembling process, it is necessary to test each chip 20 and to prevent inferior chips from being subjected to the assembling process. To this end, it is generally performed to test the electrical characteristics of the chip regions 20 in the wafer 10 before the regions are separated, and to give an identification mark to an inferior chip detected by the test.
For performing the above characteristic test of chip regions before terminals for a finished product are not provided to the regions, a method using a probe 30 made of a conductive material has been widely employed. In the method, for example, as is shown in FIG. 2, the tip of the probe 30 is brought into contact with a bonding pad 21 formed in each chip region 20. The base portion of the probe 30 is connected to a measuring apparatus such as an electrical signal generator or a waveform analyzer. Thus, the integrated circuits formed in the chip regions 20 are electrically connected to the measuring apparatus, which enables the characteristic test of the regions to be performed.
At least that tip portion of the above probe 30 which is to be brought into contact with an object is made of e.g. tungsten (W), a silver-palladium alloy (Ag-Pd), or a copper-beryllium alloy (Cu-Be). The material of the tip portion is determined in accordance with the material of the electrode pad.
Specifically, in order to be brought into contact to an aluminum electrode employed in a memory IC or a logic IC, a probe having a tip portion made of W is mainly used. Further, in order to be brought into contact to a gold bump electrode employed in an LCD driver IC or a CPU chip, a probe having a tip portion made of an Ag-Pd alloy is mainly used. In the case of a high-current source pin employed in a linear IC or a transistor, a probe having a tip portion made of Cu-be is mainly used.
However, it is difficult to obtain accurate characteristic test results by using the above-described probes, since a sufficiently low and stable contact resistance cannot be obtained between the probes and an object.
Specifically, a sufficiently low initial contact resistance cannot be obtained by using the probe having its tip portion made of W. Also, a sufficiently stable contact resistance cannot be obtained by using the same, and therefore the contact resistance will increase if the number of times of contact increases. On the other hand, the probe having its tip portion made of Ag-Pd or Cu-Be enables such a sufficiently low initial contact resistance to be obtained, but cannot maintain the low contact resistance in a stable manner, so that the contact resistance will increase if the number of times of contact increases.